The film features McGregor, Sheen and fellow actor Tom Hiddleston from The Avengers. They are joined by musicians Rita Ora, Tinie Tempah and Emma Bunton in the short clip.
The war between forces loyal to Bashar al-Assad and those seeking to oust his Ba’ath regime has been raging since March 2011.
In that time Syrians have lost their homes and fled to Lebanon, Jordan, Iraq, Turkey and North Africa. Many are living in tented settlements in refugee camps.